Comparison of the electrochemical behavior of CoCrWNi, CoCrFeNiMo, and CoNiCrMo alloys

• Published in: Journal of biomedical materials research. Part B, Applied biomaterials Vol. 108; no. 7; pp. 2971 - 2980
• Main Author: Pound, Bruce G.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.10.2020; Wiley Subscription Services, Inc
• Subjects: Alloys; Biomedical materials; Chromium; Cobalt base alloys; cobalt‐chromium alloys; cyclic potentiodynamic polarization; Electrical resistivity; Electrochemical analysis; Electrochemical impedance spectroscopy; Electrochemistry; Electrode polarization; Intermetallic compounds; Materials research; Materials science; Oxidation; Oxide coatings; phosphate‐buffered saline; Spectroscopy; Thickness; Transpassive dissolution; cobalt-chromium alloys; electrochemical impedance spectroscopy; phosphate-buffered saline; cyclic potentiodynamic polarization
• ISSN: 1552-4973; 1552-4981; 1552-4981
• DOI: 10.1002/jbm.b.34627

Numerous studies have examined the electrochemical behavior of Co‐28Cr‐6Mo and Co‐35Ni‐20Cr‐10Mo in simulated physiological solutions. However, two other CoCr alloys—Co‐20Cr‐15W‐10Ni and Co‐20Cr‐16Fe‐15Ni‐7Mo—have received relatively little attention. In this work, cyclic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of as‐received and passivated CoCrWNi and CoCrFeNiMo in phosphate‐buffered saline. Comparison of the potentiodynamic results with those for as‐received and electropolished CoNiCrMo showed marked differences in the passive behavior of the three alloys, even though they are all Co‐20Cr. The passive film on all three alloys underwent solid‐state oxidation involving Cr(III) to Cr(VI) and Co(II) to Co(III). However, the alloys then differed substantially in their behavior. CoCrFeNiMo exhibited no further changes up to the onset of water oxidation, whereas CoNiCrMo was subject to transpassive dissolution, while CoCrWNi underwent a second oxidation and then localized breakdown of the oxide. The EIS results also showed differences between the alloys with regard to the oxide thickness and resistivity. The thickness increased in the order CoCrFeNiMo < CoNiCrMo < CoCrWNi. Passivation increased the thickness but did not significantly affect the resistivity. For the as‐received alloys, the resistivity increased with thickness, suggesting that the oxide films became less defective with increasing thickness.